With the technical development of OLEDs (Organic Light Emitting Diode) and particularly the advent of the Active Matrix OLED (AMOLED), both sizes of the OLED product and the glass substrate continue to increase thus requiring constant enlargement of the size of a mask for use in manufacturing the OLED product to form film.
Conventionally, a photolithographic process for manufacturing a fine metal mask (FMM) of typically an Invar material requires equipments such as a coating machine, a high-precision exposure machine, a chemical etching machine, etc., allowing an optimum opening precision thereof at ±3 μm. However, such precision can only be reached on a small-sized substrate. As the scale of invested use of the AMOLED production line grows increasingly larger, the equipments responsible for manufacturing a mask severely lagged behind, mainly for the reason that it costs an expensive spending and excessive devotion for the research, development and manufacture of the related equipments. Moreover, a photomask needs to be pre-made for the mask being manufactured by a photolithographic process, and once a variation of the substrate layout occurs, the photomask becomes discarded. Therefore, currently the manufacture of an FMM mask by a photolithographic process is applicable only for small-sized production lines, with also a longer period and a higher cost required for the manufacture.
In a further aspect, if the precision requirement for the mask is not so high, it can be manufactured by using a laser cutting machine. In fact, for a laser cutting machine, it has by itself a remarkable precision of processing, which can reach an optimum of ±2-3 μm. However, since the thermal cutting of a metal sheet by laser causes thermal deformation easily, resulting in inability to release the accumulated stress in the metal, the metal sheet may begin to warp and turn folded very easily while being stretched into a mask, so that the flatness and the linearity of the mask can be disadvantageously affected. Consequently, a large size indeed for the substrate, such as G8.5 (a common type of substrates), may generally lead to a precision above 50 μm, or even worse.
As it can be seen, current high-precision film forming masks are confined to the metallic material (e.g. Invar) and a high cost, wherein the processing with a photolithographic process costs expensively and is not suited for large-scale production lines; a direct cutting with laser causes thermal deformation easily, by which the precision cannot be ensured and the requirement for a high-precision mask can hardly be met.
In general, after the processing is done for the mask, it requires also a stretching set for stretching the mask to ensure flatness and linearity of the mask. In the case where the precision of processing is limited, the required linearity and flatness may not be fulfilled if the tension is too much and the mask may be damaged if the tension is too small, which could result in reduced yields of the mask.